Wow, it's kind of weird to me that I'm always reading about poor quality, because I literally shop there all the time, and a great chunk of my wardrobe (probably 30-40%) is Forever 21 and I have never had any quality issues. I've bought some of everything.....from tops to dresses to bottoms to shoes, etc. I guess I've been super lucky?
Closest I can think of, is jewelry will usually lose some of its detail (like if it has little beads or crystals glued on or something) after a couple of wears, but I have also had the same experience with other jewelry at similar female clothing stores (i.e. Charlotte Russe and the like), and I feel it's fair if I'm paying 3 or 4 bucks for a super cute necklace. Obviously quality isn't going to be as lasting as a 40 dollar necklace. /shrug
But yeah, I've never had any problems with the quality. Weird.